From Imagination and Thought in the Middle Ages, by C.S. Lewis (in Studies in Medieval and Renaissance Literature, 1966).
Go out on any starry night and walk alone for half an hour, resolutely assuming that pre-Copernican astronomy is true.
You will be looking at a world unimaginably large but quite definitely finite. At no speed possible to man, in no lifetime possible to man, could you ever reach its frontier, but the frontier is there; hard, clear, sudden as a national frontier.
And secondly, because the Earth is an absolute centre, and Earthwards from any part of this universe is downwards, you will find that you are looking at the planet and stars not merely in terms of 'distance' but of that very special kind of distance we call 'height'. They are not only a long way from Earth, but a long way above it.
Now these two factors taken together - enormous but finite size, and distances which, however vast, remain unambiguously vertical, and indeed vertiginous - at once present you with something which differs from the Newtonian picture rather as a great building differs from a great jungle.
You can lose yourself in infinity; there is indeed nothing much else you can do with it. It arouses questions, it prompts to a certain kind of wonder and reverie, usually a sombre kind (...) But it answers no questions; necessarily shapeless and trackless, patient of no absolute order or direction, it leads, after a little, to boredom or despair or (often) to the haunting conviction that it must be an illusion.
But the effect of the old model becomes even more interesting when we consider order.
It is not merely very large, it is a whole of finely graded parts. Everything descends from the circumference with a steady diminution in size, speed, power and dignity. (...)
All above the Empyrean [Firmament] is in a special, immaterial sense 'Heaven', full of the divine substance.
From the Empyrean down to the Moon is the realm of aether - that strange half-matter in which so many different ages have believed (...) - changeless, necessary, not subject to Fortune.
From the Moon down to the Earth is the realm of air (...) which is also the realm of luck, change, birth, death and contingence.
It is a structure, a finished work, a unity articulated through a great and harmonious plurality. It evokes not mere wonder but admiration. It provides food for thought and satisfaction for our aesthetic nature.
After the dimensions and the order we must consider the dynamics. (...)
The infinite, according to Aristotle, is not actual. No infinite object exists; no infinite processes occur. Hence we cannot explain the movement of one body by another and so on forever. (...)
All the movements of the universe must therefore, in the last resort, result from a compulsive force exercised by something immovable.(...)
He called this Unmoved Mover either 'God' or 'Mind'. It moves the Primum Mobile [or outermost sphere of the universe] by love. (...)
Accordingly we find (not now by analogy but in strictest fact) that in every sphere there is a rational creature called an Intelligence which is compelled to move, and therefore to keep his sphere moving, by his incessant desire for God. (...)
A modern might ask why a love for God should lead to a perpetual rotation. I think, because this love or appetite for God is a desire to participate as much as possible in his nature; i.e. to imitate it. And the nearest approach to His eternal immobility, the second best, is eternal regular movement in the most perfect figure, which, for any Greek, is the circle.
[A man of the middle ages] did not think that the spaces he looked up at were silent, or dark or empty. Far from being silent, they were perpetually filled with sweet, immeasurable sound. The vast hollow spheres, turning each at its proper interval inside its superior, gave out a blended harmony.
Nor were these high regions dark. The darkness in which the stars (for us) is set is merely the darkness of the long, conical shadow cast by the earth when the sun is below our feet. They knew (...) that the apex of this dark cone must fall well above the moon.
Beyond that apex the higher heavens are bathed in perpetual sunshine.
And these spaces, bright and resonant, were also inhabited. We have already peopled them with the Intelligences who either animate or guide the spheres.
Distinct from these, but of course equally immortal and superhuman, are the angels. Their natural habitat is between the Empyrean and the Moon and their number is probably enormous. (...)
[Humans] touch only the lowest fringe of angelic life. (...) They are ordered in nine classes which are arranged in three groups of three classes each. (...)
The lowest hierarchy deals with human affairs; Principalities with the destiny of nations, Archangels and Angels, in varying ways, with those of individuals.
[God governs the world through the angels; the whole angelic population, without prejudice to its complex internal triads, is the medium between God as agent and Nature (or man) as patient.]
But I must crowd the sky a little more. (...) Besides the Intelligences and the angelic hierarchies are the planets themselves. Each of them is doing things to us as every moment.
Go back for a moment to the experience I mentioned at the beginning; that of looking up at the stars (...).
The full contrast between the medieval experience and ours is only now apparent.
For whatever else we feel, we certainly feel that we are looking out; out of somewhere warm and lighted into cold, indifferent desolation, out of a house onto the dark waste of the sea.
But the medieval man felt he was looking in.
Here is the outside. The Moon's orbit is the city wall. Night opens the gates for a moment and we catch a glimpse of the high pomps which are going on inside; staring as animals stare at the fires of the encampment they cannot enter, as rustics stare at a city, as surburbia stares at Mayfair.
These spheres are moved by love, by intellectual desire, never sated because they can never completely assimilate themselves to their object, and never frustrated because they continually do so to the fullest extent which their nature admits or requires.
Their existence is thus one of delight.
The motions of the universe are to be conceived not as those of a machine or even an army, but rather as a dance, a festival, a symphony, a ritual, a carnival, or all these in one.
They are the unimpeded movement of the most perfect impulse towards the most perfect object.